1. Field of the Invention
The present invention relates to a method and a system for coordinating at least one drive unit.
2. Description of Related Art
Drivetrains which use multiple drive units are known for vehicles. In hybrid vehicles, for example, an internal combustion engine and at least one electric motor act together as provided drive units to generate a driving torque. Multiple control units, which communicate with each other via a bus system, are used for this purpose, it being possible in many cases to use a higher-level control unit which coordinates the functions of the drive units. The drive units are then assigned one or more drive unit control units. One of the drive unit control units may additionally perform the tasks of the higher-level control unit.
The higher-level control unit is designed to coordinate functions of the drive units and to specify setpoint operating points, typically setpoint torques, for the drive units. For this purpose, the drive unit control units may transmit operating parameters as information to the higher-level control unit via the instantaneously possible operating ranges of the drive units and, if necessary, additionally via instantaneously optimum operating ranges of the drive units. The higher-level control unit uses this information as basic conditions for coordination for the purpose of setting setpoint operating points.
The instantaneously possible and optimum operating ranges of the drive units change over time, e.g., due to dynamic effects in the air system of the internal combustion engine, which may be referred to as the turbocharger lag, among other things, or due to the activation and deactivation of ancillary units which are connected to an on-board electrical system together with electric motors.
Time delays may occur in the communication between the control units, i.e., between the drive unit control units and the higher-level control units, so that the operating ranges reported by the drive units reach the higher-level control unit after a time delay. In most cases, the reported operating ranges in the higher-level control unit typically do not match the instantaneous operating ranges ascertained in the drive unit control units, since the reported operating ranges are out of date, due to the time delay in the higher-level control unit.
Consequently, the higher-level control unit usually provides the drive units with setpoint operating points which are based on these outdated, reported operating ranges. The setpoint operating points are reported by the higher-level control unit to the drive unit control units, which results in a new time delay. Due to this double delay, a setpoint operating point reported to the drive unit control unit may lie outside the instantaneously possible operating range ascertained in the drive unit control unit, which may make it impossible to provide this reported setpoint operating point, thus having a negative effect on the quality of control. Even if the reported, delayed setpoint operating point may be provided, it may lie outside an instantaneously optimum operating range ascertained by the drive unit control unit, even though the higher-level control unit has requested an optimum operating range.
A control method for a system in a motor vehicle having a central unit and a plurality of modules which are connected to the central unit is known from the published German patent application document DE 196 46 387 A1. An item of activation information is stored in each module, an item of control information being transmitted from the central unit to the modules for the purpose of activating modules. Only the addressed modules whose activation information has a predefined relationship with the transmitted control information are activated.
A method for transmitting information in motor vehicles is described in the published German patent application document DE 197 55 311 B4. At least one control unit is designed to supply information within the scope of messages, at least two operating variables, which do not occur at the same time, and at least one further item of information being supplied, the at least one further item of information being transmitted within the scope of the message for the operating variable which is not currently present.
The subject matter of the published German patent application document DE 10 2008 022 082 A1 is a method for operating a drivetrain in a vehicle which has an electric drive and an internal combustion engine. According to the method, a torque is provided for driving the vehicle by the electric drive as well as by the internal combustion engine, the internal combustion engine torque being varied within a permissible range. If the internal combustion engine is operated at an edge of the range, a check is performed to determine whether a selected operating condition may be provided by the internal combustion engine.